Indo-Pacific Walker circulation drove Pleistocene African aridification

Area of Science:

• Paleoclimatology
• Oceanography
• Climate dynamics

Background:

• Eastern African hydroclimate is linked to atmospheric Walker circulation.
• Pacific Walker circulation influenced Indian Ocean climate on glacial-interglacial timescales after 2.2-2.0 million years ago (Ma).
• Long-term records of Pacific-influenced climate transitions in the Indian Ocean were previously unavailable.

Purpose of the Study:

• To reconstruct a seven-million-year record of tropical Indian Ocean circulation.
• To determine the timing and mechanisms of Pacific-influenced climate transitions in the Indian Ocean.
• To investigate the link between Indo-Pacific Walker cells, African aridification, and hominin evolution.

Main Methods:

• Analysis of a seven-million-year record of Mozambique Channel Throughflow (MCT) flow-speed variations.
• Correlation of MCT flow speeds with the intensification of the Pacific Walker circulation.
• Development of a mechanism linking MCT flow speeds to Indo-Pacific Walker cells and African aridification.

Main Results:

• MCT flow speed was weak and steady until 2.1 ± 0.1 Ma, then increased, coinciding with Pacific Walker circulation intensification.
• MCT flow speeds showed strong increases during glacial periods and weak speeds during interglacial periods after the Mid-Pleistocene Transition.
• Increasing MCT flow speeds reflect the development of Indo-Pacific Walker cells, promoting African aridification.

Conclusions:

• The Pacific Walker circulation intensified around 2.1 Ma, significantly altering Indian Ocean circulation and African hydroclimate.
• African aridification increased after 2.1 Ma, with pronounced humid interglacial periods.
• This long-term climate record provides insights into climate-environmental drivers of hominin evolution and dispersal.